The research proposed will seek to define the molecular basis of Rh antigenicity in the human erythrocyte plasma membrane. Advances in membrane biochemistry, the promise of pilot experiments, and the availability of elegant radiolabeled antibody techniques provide reasonable expectation that the isolation of this lipid-dependent membrane protein antigen will at last be possible. Soluble antigen-antibody complexes obtained by a recently developed technique involving a new detergent will be purified to homogeneity by biochemical separation methods. This will involve chromatographic and electrophoretic procedures and will be followed by analytical characterization involving gas-liquid and ion-exchange chromatography. The relationship of the isolated polypeptide components to the known molecular anatomy of the red cell membrane will be investigated. It is proposed to study the role of the main red cell membrane polypeptide, component 3, in Rh function, as well as the nature of the membrane lesion or deletion in Rh-null cells. The physicochemical basis for the role of phospholipids and cholesterol in Rh function will be investigated in red cells of modified phospholipid and cholesterol content. Immunoelectron microscopy of isolated Rh in model lipid membranes will further our understanding of antibody-mediated antigenic redistribution and membrane dynamics. The elucidation of the molecular biology of Rh will further our understanding of this clinically important blood group and of biological membranes in general.